Telnet validate email, 550 MI:SPF error

Question

When I try validating an email through telnet, using:

Telnet MX.server.for.email.i.want.to.validate.com 25

HELO Buddy

MAIL FROM:  example email address 

I get a 550 MI:SPF error, telling me that my IP address does not match the valid sender. In other words, it looks like a spoofed email.

Given that I'm just running Telnet from my Windows desktop, how do I set up a valid request to validate emails with?

Are there any email services that can relay through Telnet to check the validity of an email address without sending an email?

Answer 1

Unfortunately you are running into a minefield.

The reason you are having an issue is because the domain name for YOUR email has a restriction saying you cant send email this way (Your domain has an SPF record saying you cant send email except from certain servers). Modifying your SPF record - which is not a great idea - will allow you to bypass this issue.

Telnet is a protocol that does little more then open a tcp session on a given port There is no concept of relaying mail through it - only opening a tcp connection.

There are websites like mxtoolbox.com that can help with all sorts of testing of mail related.issues.

Most mail servers have disabled user verification because it attracts spammers and reduces security, so you often cant check the validity if an email address without sending an email.

Answer 2

I get a 550 MI:SPF error, telling me that my IP address does not match the valid sender. In other words, it looks like a spoofed email.

Of course it does – you're trying to use someone else's address in the Envelope-From. That's practically the definition of spoofed.

Given that I'm just running Telnet from my Windows desktop, how do I set up a valid request to validate emails with?

Specify the test address as the recipient, i.e. in RCPT.

For the sender, instead use an address belonging to a domain that either allows your desktop PC's IP address, or doesn't have SPF restrictions at all. Ideally this should be a domain that you actually have the rights to. (Note that subdomains can have their own SPF records independently from the parent domain.)

Are there any email services that can relay through Telnet

"relay through telnet" is a nonsensical requirement. Mail delivery over SMTP does not involve Telnet at all.

You're just using the telnet command because it also works as a raw TCP client, but other software and services have no need for this – they make their own TCP connections through the OS, and they directly send the same commands that you're typing in.